1. Field of the Invention
The present invention relates to a robot hand structure, of an industrial robot, for handling a workpiece and to a handling robot system having the same.
2. Description of the Related Art
An industrial robot for performing a handling operation is intended to handle not one type of workpiece, but, in most cases, different types of workpieces of different shapes and sizes. For this reason, operation requirements often cannot be met by a robot system having only one type of robot hand (hereinafter referred to simply as a “hand”) prepared for grasping a workpiece. Also, in the case that a single type of workpiece is handled, a portion of the workpiece to be grasped may be required to be changed depending on a specific requirement of a handling operation. In this case, if the shape of the held portion of the workpiece is different before and after the change, a single type of hand, similarly, cannot meet the requirements suitably. Further, in the case that a grasping claw is required to have a shape conforming to the shape of the workpiece, it is difficult to perform the handling operation with a single hand.
In order to address such a situation, it has conventionally been the common practice to prepare a plurality of types of hands in accordance with the number of workpiece types or the number of operation types. Each of the prepared hands often has built therein the required number of grasping claws (grasping members), an actuator for causing the grasping claws to perform the grasping operation (such as motor, air cylinder, etc.), and a drive mechanism for driving the grasping claws with the actuator. To change the hand, on the other hand, a hand retaining unit for changing a hand is widely used. In the case that a plurality of types (three types in this case) of workpieces 6, 7, 8 having different shapes are handled, for example, using a handling robot (robot mechanical part) 1 having six degrees of freedom (axes) as shown in FIG. 1, different hands 3, 4, 5 suitable for grasping the different workpieces are used to execute different types of handling operations.
The hand retaining unit 2 is arranged at a forward end of an arm of the handling robot (hereinafter sometimes referred to simply as the “robot”) 1, and one of the prepared hands 3 to 5 is mounted on the robot via the hand retaining unit 2. FIG. 1 shows the workpiece 6 being grasped by the hand 3 mounted on the robot. Each of the hands 3 to 5 has built therein grasping claws having an arrangement, shape and size suitable to grasp one of the workpieces 6 to 8, and an actuator to cause the grasping claws to perform the grasping operation. Drive mechanisms for moving the robot 1 along each of axes thereof are controlled by a robot control unit (not shown) in a well-known manner, while the hand retaining unit 2 and the actuators for the hands to perform the grasping operation are also controlled by the robot control unit.
When the hand is changed (for example, the hand 3 is replaced with the hand 4), the robot 1 is moved, for example, to an access point to a fixation holder for the hand 3, and a hand release command is sent from the robot control unit to the hand retaining unit 2 to release the hand 3 and bring the hand 3 back to the fixation holder for the hand 3. Then, the robot 1 is moved, for example, to another access point to a fixation holder for the hand 4, to engage the hand retaining unit 2 with the hand 4, and a command to lock the hand 4 is sent from the robot control unit to the hand retaining unit 2. In this way, the hand 3 is completely replaced with the hand 4. The hand retaining unit 2 is also equipped with a mechanism for connecting or disconnecting a signal line system, etc., to the actuator built in each hand when the hand is replaced.
However, in the case that the hand including the grasping claws, the actuator and the drive mechanism for the grasping claws is changed to deal with a great variety of shapes, etc., of the workpieces, as in the prior art described above, a problem may be caused in which both the actuator and the drive mechanism are liable to interfere with devices surrounding the workpiece in a wide area so that the handling operation may be hampered. For example, in the case that ten types of hands are prepared for a hand changing, nine hands other than the hand in use exist in an operation range of the robot and occupy a considerable volume of space, resulting in an increased risk of interference.
An attempt to handle a plurality of types of workpieces with a few types of hands, on the other hand, would cause a problem in which the shape, etc., of the grasping claw may fail to conform to the shape of a particular workpiece, thereby resulting in an increased possibility of the workpiece being grasped erroneously or dropped. Further, in the case that a grasping claw having a shape suitable for a particular workpiece having a unique shape is required, it is necessary to prepare a hand having dedicated grasping claws having the shape suitable for each type of the workpieces, thereby increasing the system cost.